Oxygen-18 isotope effects will be studied for yeast hexokinase using 6-180-fructose and the coupled equilibrium perturbation technique. Kinetic and equilibrium isotope effects will be measured for enolase and aconitase. The pH variation of V, V/K, and primary and seconnary isotope effects will be measured for aspartase. Isotope effects will be measured with either glucose or glucose-6-p as substrates with glucose-6-p dehydrogenase. The mechanism of the ATPase reaction of phosphofructokinase will be investigated by determining the isotope effect on the Michaelis constant of the activator, 2,5-anhydromannose-6-P, when it is deuterated on the aldehyde carbon.